1. Field of the Invention
The present invention relates to a spread illuminating apparatus used as an illuminating means for signboards, various kinds of reflection-type display devices and the like, and more particularly, to a spread illuminating apparatus used as an illuminating means for a reflection-type liquid crystal display device.
2. Description of the Related Art
A liquid crystal display apparatus, which is characterized by being thin, small in occupied volume and lightweight, is used for many kinds of electric appliances such as a portable telephone, a personal computer or the like. Since a liquid crystal of the liquid crystal display device does not emit light by itself, when the liquid crystal display device is used in a dark place where sunlight or room light is not sufficiently available, a separate illuminating apparatus for lighting the liquid crystal is required besides the liquid crystal display device. Accordingly, it is desirable that such an illuminating apparatus is also small in size and low in power consumption. In order to attain this, light from the illuminating apparatus must be efficiently used. A conventional spread illuminating apparatus to answer such a demand is shown in FIG. 10 as an example.
As shown in the figure, a spread illuminating apparatus 1xe2x80x2 generally comprises a transparent substrate 2 formed of a light-transmissible material and a light source 5 disposed close to an end surface 8 of the transparent substrate 2. The spread illuminating apparatus 1xe2x80x2 makes light beams emitted from the light source 5 enter the transparent substrate 2 to light a liquid crystal display device (not shown in the figure) disposed under the transparent substrate 2.
The light source 5 comprises a long plate-like light conductive member 3 formed of a transparent material and a spot-like light source (for example, light emitting diode) 4 disposed at an end of the light conductive member 3 and mounted on a flexible printed circuit board 6. The light conductive member 3 is formed in a so-called wedge-shape, in which its thickness gradually decreases as it gets away from the spot-like light source 4. Further, the light conductive member 3 is provided with an optical path conversion means 12. The optical path conversion means 12 is formed on a surface opposite to a surface 9 facing the end surface 8 of the transparent substrate 2, and comprises grooves 10 triangular in section and plane portions 11 adjacent to the grooves 10. Light beams emitted from the spot-like light source 4 disposed at the end of the light conductive member 3 are adapted to enter substantially uniformly the end surface 8 of the transparent substrate 2 thanks to the wedge-shaped light conductive member 3 and the optical path conversion means 12. Note that the light conductive member 3 is disposed at a predetermined distance from the end surface 8 of the transparent substrate 2 in such a manner that the surface 9 of the light conductive member 3 is aligned to the end surface 8 of the transparent substrate 2.
A frame 13 is provided around the light conductive member 3 so that the light beams emitted from the spot-like light source 4 can enter efficiently the transparent substrate 2. The frame 13 is formed substantially in C-shape and covers longitudinal surfaces of the light conductive member 3 except the surface 9 facing the transparent substrate 2. The frame 13 is disposed in such a manner that a part of an upper plate inner surface 14 and a part of a lower plate inner surface 15 of the frame 13 overlap a part of the transparent substrate 2 at the end surface 8 side (see FIG. 12). A hard plastic to which a film evaporated with metal such as silver, a white-color film or the like is attached, or a bent metal plate such as an aluminum plate or a stainless plate is pasted on the sides of the frame 13 that face the light conductive member 3 (inner surfaces).
The transparent substrate 2 is formed in a so-called wedge-shape, in which its thickness gradually decreases as it gets away far from the end surface8. Further, a light reflection pattern 19 is formed on an upper surface 16 of the transparent substrate 2. The light reflection pattern 19 comprises grooves 17 triangular in section and plane portions 18 adjacent to the grooves 17. Then, light beams coming from the light conductive member 3 are reflected uniformly on the whole surface of the transparent substrate 2 irrespective of the distance from the light conductive member 3 and illuminate the liquid crystal display device (not shown) disposed under the transparent substrate 2.
Moreover, a reflection preventive film 20 is attached to a lower surface of the transparent substrate 2. Even when light from the light source 5 is not used, that is, sunlight, room light or the like is used, the light does not cause diffused reflection inside the transparent substrate 2 because of the reflection preventive film 20, and illuminates the liquid crystal display device disposed under the transparent substrate 2. Thus, good images can be displayed on a liquid crystal screen.
By the way, in the spread illuminating apparatus 1xe2x80x2 structured as described above, it is desirable that the areas of the opposing surfaces of the transparent substrate 2 and the light conductive member 3 are set equal to each other in order that the light beams emitted from the spot-like light source 4 are most efficiently transmitted into the transparent substrate 2. In other words, when the dimension of the end surface (incident surface) 8 of the transparent substrate 2 and the dimension of the surface (exit surface) 9 of the light conductive member 3 that faces the incident surface 8 are equal to each other, the light beams can be most efficiently transmitted from the exit surface 9 to the incident surface 8. However, because the reflection preventive film 20 is attached to the lower surface of the transparent substrate 2, when the dimension of the incident surface 8 and the dimension of the exit surface 9 are set equal to each other, the thickness of the transparent substrate 2 turns out to be larger than the thickness of the light conductive member 3 by the thickness t of the reflection preventive film 20 (see FIG. 11). In this state, if the light conductive member 3 and the transparent substrate 2 are simply set in the frame 13, the exit surface 9 shifts off (slides down) relative to the incident surface 8 by the thickness t of the reflection preventive film 20 as shown in FIG. 12. Therefore, it does not happen that light beams emitted from the exit surface 9 enter most efficiently the incident surface 8, and a part of the light beams emitted from the exit surface 9 enters the reflection preventive film 20. If the light beams enter the reflection preventive film 20, the end portion of the reflection preventive film 20 is reflected in the liquid crystal screen thereby generating an unevenness in brightness. Accordingly, in order to transmit light in the most efficient manner, the exit surface 9 and the incident surface 8 must face each other in an accurately matching position.
The present invention has been made in view of the above, and an object of the present invention is therefore to provide a spread illuminating apparatus in which a light source (light conductive member) can be positioned accurately and easily in the thickness direction relative to a transparent substrate thereby presenting a good liquid crystal display.
In order to solve the above problem, according to a first aspect of the present invention, there is provided a spread illuminating apparatus comprising a bar-like light source disposed close to an end surface of a transparent substrate formed of a light-transmissible material, characterized in that a frame is provided in such a manner as to cover the bar-like light source and a portion of the transparent substrate to which the bar-like light source is disposed close, and that the frame is provided with a positioning means for determining the position of the bar-like light source relative to the transparent substrate in the thickness direction. According to the present invention, the end surface of the transparent substrate and the surface of the bar-like light source, which face each other, are disposed in such a manner that the surfaces oppose each other at a predetermined distance in an exactly matching position due to the positioning means. Thus, light is transmitted with a high efficiency.
Here, the positioning in the thickness direction refers to the positioning of the end surface of the transparent substrate and the surface of the bar-like light source, which face each other, in the short-side direction.
Further, in order to solve the above problem, according to a second aspect of the present invention, the spread illuminating apparatus is characterized in that bent springs are provided as the positioning means. The bent springs are disposed on an inner surface of the frame where the bar-like light source is to sit and the bar-like light source in the frame is pushed up in the thickness direction and fixedly positioned at a place where the surface of the bar-like light source coincides with the end surface of the transparent substrate, whereby the light from the light source is transmitted to the transparent substrate efficiently.
Moreover, in order to solve the above problem, according to a third aspect of the present invention, the spread illuminating apparatus is characterized in that wrinkles are provided as the positioning means. With the wrinkles provided as the positioning means, the surface of the bar-like light source and the end surface of the transparent substrate can coincide accurately with each other simply by setting the bar-like light source into the frame. Thus, the light from the light source can efficiently be transmitted to the transparent substrate.
In addition, in order to solve the above problem, according to a fourth aspect of the present invention, the spread illuminating apparatus of the present invention is characterized in that the frame is bent to have a step as the positioning means. Due to the step provided on the frame, the positional relationship between the bar-like light source and the transparent substrate both disposed in the frame is exactly determined.
Furthermore, in order to solve the above problem, according to a fifth aspect of the present invention, the spread illuminating apparatus is characterized in that a spacer is provided as the positioning means on an inner surface of the frame where the bar-like light source is to sit. The spacer can be with an arbitrary thickness, and due to the spacer the positional relationship between the bar-like light source and the transparent substrate is accurately determined.